When did the Earth Day tradition start?

Earth Day, a day for promoting conservation and environmental awareness of Earth’s resources, had its first international observance April 22, 1970, in North America and Western Europe. The international Earth Day was the culmination of student-led campus environmental movements in the 1960s.
During the years, there has been some dispute that the vernal (spring) equinox is the “true” Earth Day. In 1970, San Francisco celebrated Earth Day on March 21. In the 40 years since, April 22 has gradually become the accepted Earth Day.